COLUMBIA  LIBRARIES  OFFSITE 

HEALTH  SCIENCES  STANDARD 


UTRITION  OF  THE  FETUS 

BY  Jl  MORRIS  SLEMONS,  M.D. 


THE  NUTRITION  OF  THE  FETUS 


THE 
NUTRITION  OF  THE  FETUS 

BY 
J.  MORRIS  SLEMOXS 


NEW  HAVEN 
YALE  UNIVERSITY  PRESS 

LONDON:   HUMPHREY  MILFORD:  OXFORD  UNIVERSITY  PRESS 

MDCCCCXIX 


~j?S-  too 


Copyright,  1919,  by 
The  American  Journal  of  Obstetrics 

Copyright,  1919,  by 
Tale  University  Press 


PRmitD  i^^  U.S.A. 


THE  INVESTIGATIONS 

BY  THE  AUTHOE  AND  HIS  COLLABOEATOES 

WHICH  AEE  THE  BASIS  OF  THIS  EEPOET 

WEEE  JklADE  IN  THE 

DEPAETMENT  OF  OBSTETEICS  AND  GYNECOLOGY 

YALE  MEDICAL  SCHOOL 

THEOUGH  THE  USE  OF 

THE  JULIA  E.  BEOOKEE  FUND 


Digitized  by  tine  Internet  Arciiive 

in  2010  witii  funding  from 

Open  Knowledge  Commons 


http://www.archive.org/details/nutritionoffetusOOslem 


THE  NUTEITION  OF  THE  FETUS* 

Pkegnan-cy  is  essentially  a  problem  in 
nutrition,  and  at  this  time  the  dominant 
metabolic  forces  are  those  which  favor 
growth.  The  mother's  gradual  but  con- 
sistent gain  in  weight  amounts  finally  to 
about  30  pounds;  exceptionally,  it  is  as 
little  as  10  to  15  pounds,  and  at  the  other 
extreme  as  much  as  40  to  50  pounds.  With 
individuals  inclined  to  be  stout  the  in- 
crease is  greater;  and  it  is  relatively 
greater  in  later  pregnancies  than  in  the 
first.  During  the  early  months  of  gesta- 
tion the  weight  generally  remains  station- 
ary or  suffers  a  slight  loss;  even  in  those 
instances  in  which  the  weight  begins  to 
increase  shortly  after  conception,  the  gain 
is  less  marked  in  the  early  months  than 
later.  For  the  last  three  months  the  aver- 
age monthly  gain  has  been  found  to  be  be- 
tween 3.5  and  5.5  pounds. 

The  mother's  increase  in  weight  is  at- 

*The  Oration  in  Obstetrics  before  the  Ontario  Medi- 
cal Association  at  Toronto,  May,  1919.  Eeprinted  from 
the  American  Journal  of  Oistetrics. 


8      THE  NUTRITION  OF  THE  FETUS 

tributable  in  part  to  the  fetus,  the  placenta, 
the  amniotic  fluid,  the  uterus,  and  the 
breasts;  but  to  some  extent  all  the  ma- 
ternal tissues  respond  to  the  stimulus 
toward  growth.  Probably  the  relative  im- 
portance of  this  last  factor  is  too  easily 
overlooked,  for,  naturally,  the  special  de- 
velopment of  the  ovum  first  seizes  upon 
and  is  likely  to  monopolize  the  attention. 
On  the  other  hand,  the  extent  of  the  par- 
ticipation of  the  mother's  body  in  the 
growth  of  the  gestation  period  may  be 
shown  by  a  simple  arithmetical  calculation. 
Thus,  if  the  weight  of  the  product  of  con- 
ception at  full  term  together  with  that  of 
the  parturient  uterus  is  deducted  from  the 
mother's  total  gain  in  weight,  it  appears 
that  only  about  half  of  her  increase  is  ac- 
counted for.  Obviously,  the  remainder 
must  be  ascribed  to  her  body  tissues  in 
general.  This  fact  suggests  the  correct 
answer  to  a  question  which  physiologists 
have  often  submitted  to  experiment, 
namely,  ^'Does  the  material  provided  for 
the  growth  of  the  ovum  come  from  the 
mother's  tissues  or  from  her  food?" 


At  first  it  was  believed  that,  for  the 
mother,  pregnancy  constituted  a  period  of 
sacrifice  and  that  fetal  growth  occurred 
at  the  expense  of  her  tissues.  Exception- 
ally, if  the  mother's  food  is  inadequate, 
this  may  be  true.  It  is  conceivable,  too, 
that  small  amounts  of  various  materials 
derived  from  the  mother's  tissues  may  be 
contributed  reg-ularly  to  the  ovum  while 
its  implantation  is  in  progress,  but  in  a 
quantitative  sense  the  requirements  of  the 
very  early  stages  of  development  are  neg- 
ligible, and  the  period  itself  is  a  brief  one, 
probably  no  longer  than  the  time  required 
for  adjustment  between  the  blastocyst  and 
the  uterine  circulation. 

With  data  at  hand  to  support  it,  the  cur- 
rent view  holds  that  pregnancy  repre- 
sents for  the  mother  a  period  of  gain, 
rather  than  of  sacrifice,  and  accordingly 
that  her  tissues  are  not  deprived  of  ma- 
terial to  supply  the  new  organism.  Both 
animal  experiments  and  observations  upon 
women   indicate   that   the   mother's    food 


10    THE  NUTRITION  OF  THE  FETUS 

furnishes  the  substances  incorporated  in 
the  body  of  the  fetus.  Thus,  in  the  case 
of  dogs,  elaborate  analyses  of  the  food  on 
the  one  hand  and  of  the  excreta  on  the 
other  teach  that  a  notable  storage  of  the 
foodstuffs  is  characteristic  of  pregnancy. 
Furthermore,  if  this  storage  is  compared 
with  the  amount  of  material  contained  in 
the  bodies  of  the  young  it  appears  that  the 
mother's  food  is  sufficient  not  only  to  meet 
her  own  requirements,  but  also  those  of 
fetal  development.  Similar  studies  in 
which  Bar  selected  rabbits  as  the  subject 
of  experiment  led  to  an  identical  conclu- 
sion. And  with  regard  to  women,  Wilson 
concludes  from  his  extensive  studies  of 
nitrogenous  metabolism  during  pregnancy 
that  an  ordinary  diet  pro\ddes  for  every 
fetal  requirement  and  permits  storage  to 
begin  in  the  maternal  organism  at  a  much 
earlier  period  than  was  generally  sup- 
posed ;  perhaps  it  begins  at  the  very  outset 
of  pregnancy. 

What  are  the  substances  required  for 
fetal  nutrition  ?  This  question  may  be  an- 
swered in  two  ways.  On  the  one  hand,  we 
may  infer  the  needs  of  the  fetus  from  those 
of  the  newborn  infant  which,  of  course,  is 


THE  NUTRITION  OF  THE  FETUS     11 

sustained  by  its  mother's  milk,  a  fluid  of 
familiar  composition.  Or,  on  the  other 
hand,  npon  the  fair  assumption  that  the 
substances  found  in  the  fetus  represent 
its  requirements  for  growth  we  may  resort 
to  the  analysis  of  its  body.  From  informa- 
tion of  this  kind  we  conclude  that  there  is 
no  great  difference  between  the  fetus  and 
the  adult  so  far  as  the  equality  of  the  food 
they  require  is  concerned :  in  their  life 
processes  both  use  the  same  organic  and 
inorganic  substances  which  are  always 
available  in  the  circulating  blood  of  the 
mother. 

The  constitutents  of  the  mother's  blood 
include  nutrient  nitrogenous  substances, 
carbohydrate,  fat,  oxygen,  water,  and  in- 
organic salts;  together  these  meet  all  the 
requirements  for  tissue  growth  and  en- 
ergy production.  That  they  are  at  the  dis- 
posal of  the  fetus,  there  can  be  no  question. 
but  it  is  equally  certain  that  none  of  these 
materials  may  pass  directly  into  its  circu- 
lation. Across  the  path  traversed  by  these 
substances  on  their  way  from  the  parent  to 
her  offspring  lies  a  complex  organ,  the 
placenta,  composed  partly  of  a  specialized 
uterine  tissue  but  mainlv  of  elements  de- 


12    THE  NUTRITION  OF  THE  FETUS 

rived  from  the  luxuriant  development  of  a 
portion  of  the  fetal  membranes — the  cho- 
rion frondosum.  The  obstructive  action  of 
the  placenta  was  demonstrated  by  the  ex- 
periments of  John  and  William  Hunter. 
These  investigators  proved  that  the 
mother's  blood  never  enters  the  fetus  and 
also  that  the  reverse  phenomenon  is  impos- 
sible. More  recently,  and  especially  after 
the  invention  of  the  microscope  and  im- 
provements in  histological  technique,  em- 
bryology has  gradually  accumulated  the 
facts  which  now  make  the  chapter  on  the 
morphology  of  the  placenta  both  intimate 
and  nearly  complete. 

The  architectural  arrangement  of  this 
organ  which  accommodates  simultaneously 
the  fetal  and  maternal  circulations,  vet 
holds  them  apart,  is  so  well  known  that 
there  is  no  longer  any  doubt  regarding  the 
path  each  follows.  Venous  blood  from  the 
fetus  enters  the  placenta  by  way  of  the  um- 
bilical arteries,  which  divide  again  and 
again  to  form  a  multitude  of  capillaries. 
Subsequently,  these  reunite  into  a  single 
vessel,  the  umbilical  vein,  through  which 
the  arterialized  blood  returns  to  the  fetal 
heart. 


THE  NUTRITION  OF  THE  FETUS    13 

Chiefly  by  the  division  and  subdivision 
of  the  fetal  vessels  in  the  placenta,  an  ex- 
tensive vascnlar  bed  is  created.  The  bed 
is  notably  enlarged  by  the  arrangement  of 
the  smallest  of  these  vessels,  which  form 
loops  hanging  toward  the  maternal  blood. 
With  this,  however,  the  fetal  vessels  do  not 
come  into  direct  contact,  for  they  are 
covered  with  connective  tissue  and  this  in 
turn  with  embryonic  epithelium.  To- 
gether with  their  enclosing  layers  of  tissue 
the  capillary  loops  constitute  the  chorionic 
villi.  During  the  early  months  of  preg- 
nancy the  epithelial  covering  of  the  villi 
forms  two  layers  but  later  is  reduced  to  a 
single  layer  of  about  the  thickness  of  endo- 
thelium. Thus,  the  thickness  and  complex- 
ity of  the  placental  partition  varies  in- 
versely with  the  nutritional  requirements 
of  the  new  organism,  for  at  first  the 
material  requirements  of  the  embryo  are 
infinitesimal.  Although  they  increase 
gradually,  these  requirements  are  insig- 
nificant in  a  quantitative  sense  until  after 
the  18th  to  20th  week  of  pregnancy;  and 
about  this  time  also  the  simplification  of 
the  placental  partition  takes  place.  In- 
deed, it  is  not  unlikely  that  the  anatomical 


14    THE  NUTRITION  OF  THE  FETUS 

transition  is  intended  to  promote  the 
physiological  interchange  between  the  fetal 
and  maternal  circulations,  thus  to  secure 
for  the  new  organism  a  more  rapid  rate  of 
growth. 

The  maternal  blood,  which  supplies  the 
fetus  with  everything  it  needs  and  coinci- 
dently  removes  its  excretory  products,  en- 
ters the  placenta  through  the  branches  of 
the  uterine  arteries  and  departs  through 
the  uterine  veins.  As  it  passes  through 
this  organ,  the  mother's  blood  comes  into 
contact  T^ith  the  surface  of  the  villi  where 
the  requisite  exchange  of  foodstuffs  and 
waste  products  takes  place.  Certain  sub- 
stances pass  in  one  direction  while  others 
are  passing  in  the  opposite  direction;  but 
all  traverse  the  same  placental  partition 
which,  as  we  have  seen,  consists  in  the 
latter  half  of  pregnancy  of  a  thin  covering 
of  epithelium,  a  layer  of  connective  tissue 
and,  ^vithin  this,  the  delicate  wall  of  the 
fetal  capillary. 

How  substances  pass  through  the  pla- 
cental partition  is  a  question  answered, 
thus  far,  only  hypo  the  tically.  There  has 
been  no  lack  of  speculation  on  the  subject. 
In  the  main  two  antagonistic  theories  have 


THE  XriRITIOX  OF  THE  FETUS     15 

been  deYeloped:  one  of  these,  the  vitahstic, 
assumes  that  the  wall  of  the  chorir^nic  vil- 
lus takes  an  active  part  in  the  placental 
interchange;  the  other,  the  meo^aii:s::c', 
regards  this  wall  as  a  passive,  semi-perme- 
able membrane  conforming  with  the  laws 
of  osmosis  and  di:ffnsion. 

1.  The  Vitalistic  Hypofh.esls.  That  the 
placenta  actnally  digests  the  food  of  the 
fetus  was  suggested  by  William  Harvey, 
who  attempted  to  establish  a  complete 
analogy  between  the  chorionic  and  the 
intestinal  villi.  This  view  gained  many  ad- 
herents after  Hofbauer  and  others  demon- 
strated the  presence  of  enzymes  in  the 
placenta,  though  it  was  never  shown  that 
these  lipolytic,  diastatic,  and  proteohnic 
enzymes  are  agents  in  the  placental  i::ter- 
change.  On  the  contrary,  it  is  Hkely  that 
they  have  to  do  only  with  the  living  pro- 
cesses  of  the  cells  which  contain  them. 

2.  The  Mechanistic  Hi/pofhe sis.  In  the 
transmission  of  a  few  substances,  it  has 
been  positively  proved  that  the  plaj-ntal 
partition  plays  a  passive  role  and  behaves 
as  a  semi-permeable  membrane.  Thus, 
oxygen  and  carbon  dioxide,  we  are  taught 
by    the    experiments    of    Cohnstein    and 


16    THE  NUTRITION  OF  THE  FETUS 

Zuntz,  pass  equally  well  from  mother  to 
fetus  or  in  the  opposite  direction,  and  al- 
ways move  from  the  point  of  higher  to  that 
of  lower  concentration.  Probably  the  laws 
of  diffusion  apply  to  the  placental  trans- 
mission of  the  anaesthetics,  chloroform, 
ether,  and  nitrous  oxide;  though  they  do 
not  apply  to  gases,  like  carbon  monoxide, 
which  enter  into  chemical  combination 
with  haemoglobin.  Cohnstein  and  Zuntz 
found  also  that  sodium  chloride  passed  the 
placenta  by  osmosis.  The  evidence  they 
obtained  relative  to  the  transmission  of 
glucose  was  not  conclusive,  though  it 
seemed  likely  that  osmosis  was  the  process 
concerned. 


II 

One  fundamental  fact  regarding  pla- 
cental transmission  was  established  by  the 
experiments  of  Gusserow  and  his  associ- 
ates, namely,  provided  the  placenta  is 
normal,  no  insoluble  substance  may  pass  it. 
The  formed  elements  of  the  blood  are  con- 
fined to  that  circulation  in  which  they 
originate;  consequently,  an  infant  whose 
mother  is  suffering  from  leukaemia,  pre- 
sents a  normal  blood  picture.  Moreover, 
cinnabar,  barium  sulphate,  and  other  insol- 
uble compounds,  when  introduced  into 
either  the  mother  or  the  fetus,  are  effectu- 
ally confined  within  the  circulation  where 
they  are  introduced.  On  the  other  hand, 
a  variety  of  soluble  substances  when  in- 
jected into  the  mother  may  be  detected 
later  in  the  fetus ;  and  the  reverse  experi- 
ment yields  analogous  results.  From  re- 
ports of  such  tests,  Kehrer  stated  in  1907 
that  of  73  substances  examined  43  were 
found  to  pass  readily  through  the  placenta. 
Many  of  the  latter  substances  are  poison- 
ous  and,  indeed,  were   selected  for  that 


18    THE  NUTRITION  OF  THE  FETUS 

reason,  because  a  toxic  action  often  assists 
in  determining  the  result  of  such  an  experi- 
ment. Thus,  strychnine,  hydrocyanic  acid, 
nicotine,  curare,  pilocarpine,  physostig- 
mine,  phloridzine,  sodium  sulphate,  methy- 
lene blue,  and  epinephrine  have  been  dem- 
onstrated in  the  mother  after  they  were 
injected  into  the  fetus. 

With  the  exception  of  carbon  dioxide,  no 
fetal  excretory  product  has  been  the  sub- 
ject of  serious  investigation.  The  sugges- 
tion of  Halban  and  Fleck,  that  the  chori- 
onic villi  elaborate  an  internal  secretion 
which  controls  fetal  excretion,  proceeds 
entirely  from  theoretical  considerations. 
^'At  present,"  we  read  in  ^'Doderlein's 
Handbuch  der  Geburtshiilfe  (1915),"  '4t 
is  impossible  to  say  more  than  that  fetal 
waste  products  make  their  way  to  the  pla- 
centa and  through  it  reach  the  maternal 
organism  which  subsequently  eliminates 
them.  ^ ' 

Since  so  little  is  known  of  the  principles 
involved  in  the  placental  interchange,  and 
direct  study  of  the  problem  by  means 
of  animal  experimentation  is  limited  by 
almost  insurmountable  difficulties,  we  have 
turned  to  clinical  observations  in  the  hope 


THE  NUTRITION  OF  THE  FETUS    19 

of  learning  what  is  the  character  of  the 
mechanism  in  question.  We  secured  speci- 
mens of  maternal  and  fetal  blood  simulta- 
neously, just  after  the  infant  was  born. 
The  fetal  blood  was  obtained  from  the  pla- 
cental end  of  the  severed  cord,  the  mater- 
nal from  one  of  the  veins  in  the  forearm. 

Current  methods  of  chemical  analysis 
yield  accurate  results  even  with  small 
specimens  of  blood.  Therefore,  at  times, 
in  a  given  specimen  we  were  able  to  es- 
timate a  number  of  its  ingredients,  but 
more  frequently  we  were  restricted  to  the 
estimation  of  one  or  two.  Although  this 
limitation  has  made  progress  slow,  it  has 
had  the  effect  of  increasing  the  number  of 
cases  studied  and  thus  broadened  our  ex- 
perience. We  have  gathered  data,  thus 
far,  relative  to  the  organic  foodstuffs,  pro- 
tein, carbohydrate,  and  fat;  and  it  will  be 
convenient  to  discuss  them  separately,  in 
the  order  named,  considering  the  waste 
products  of  nitrogenous  metabolism  along 
with  the  foodstuffs  from  which  they  are 
derived. 


Ill 

Pkotein,  distinguished  among  the  food- 
stuffs because  it  contains  the  chemical  ele- 
ment, nitrogen,  may  not  be  utilized  di- 
rectly by  our  tissues.  Intestinal  digestion 
breaks  down  protein  into  much  simpler  ni- 
trogenous compounds,  the  amino  acids, 
which  are  absorbed  into  the  blood  stream 
and  distributed  to  every  part  of  the  body. 
The  amino  acids  are  used  both  for  con- 
struction and  repair ;  and,  according  to  the 
organ  which  employs  them,  they  are  built 
into  one  variety  of  protein  or  another, 
probably  of  a  very  different  character 
from  that  of  the  protein  in  the  diet  which 
originally  supplied  them. 

Now,  tissue  metabolism,  which  is  the 
name  given  the  intricate  and  poorly  under- 
stood phenomenon  just  referred  to,  has 
another  side.  As  long  as  life  lasts  tissue 
protein  is  being  torn  down,  or  perhaps 
burned  down,  with  the  result  that  chemical 
compounds  are  formed  which  our  bodies 
are  incapable  of  utilizing;  therefore,  they 
are  called  waste  products.     These  com- 


THE  NUTRITION  OF  THE  FETUS    21 

NON-PEOTEIX  NITEOGEI^  AND  UEEA 
NITEOGEX 

OP   THE   TVHOLE   BLOOD 


No. 

Source 

Para 

N.P.N. 

mg.per 
lOOcc. 

Urea- 
nitro- 
gen 
mg.  per 
100  cc. 

Remarks 

1 

Mother 
Fetus 

I 

20.2 
20.5 

9.3 
8.9 

No  anaesthetic. 

2 

Mother 
Fetus 

I 

26.5 
27.2 

9.8 
10.7 

Whiffs  of  chloroform. 

3 

Mother 
Fetus 

I 

21.7 
20.0 

9.3 

8.4 

WhifFs  of  chloroform. 

4 

Mother 
Fetus 

I 

20.0 
19.0 

9.8 
11.7 

Deep  chloroform. 

5 

Mother 
Fetus 

n 

22.5 
22.0 

9.8 
9.8 

No  anaesthetic. 

6 

Mother 
Fetus 

n 

23.5 
20.0 

10.3 
8.9 

No  anaesthetic. 

7 

Mother 
Fetus 

n 

21.7 
21.7 

10.2 
9.3 

No  anaesthetic. 

8 

Mother 

Fetus 

n 

21.2 
i2!5 

8.9 
10.3 

Whiffs  of  chloroform. 

9 

Mother 
Fetus 

n 

28.2 
26.5 

13.5 
12.1 

"Whiffs  of  chloroform. 

10 

Mother 
Fetus 

n 

19.5 
19.2 

8.4 
7.9 

Whiffs  of  chloroform,  i 

11 

Mother 
Fetus 

n 

18.5 
18.5 

8.4 
9.3 

Whiffs  of  chloroform. 

12 

Mother 
Fetus 

in 

26.5 
27.5 

10.8 
11.7 

VV  hiffs  of  chloroform. 

1 

13 

Mother 
Fetus 

B' 

27.7 
27.2 

13.1 
13.5 

Whiffs  of  chloroform. 

14 

Mother 
Fetus 

V 

29^7 
24.2 

14.0 
13.5 

Whiffs  of  chloroform.! 

15 

Mother 
Fetus 

\'  1 1 1 

27.7 
24.7 

11.2 

9.8 

No  anaesthetic. 

16 

Mother 
Fetus 

IX 

27.7 
27.5 

12.6 
11.7 

Whiffs  of  chloroform. 

22    THE  NUTRITION  OF  THE  FETUS 

pounds,  too,  are  much  simpler  in  structure 
than  protein  though,  like  it,  they  are  char- 
acterized by  the  presence  of  nitrogen  in 
their  molecules. 

Besides  certain  well-known  proteins, 
then,  our  blood  contains  a  number  of  other 
nitrogenous  substances.  Perhaps,  it  is 
fair  to  regard  the  blood  protein  as  reserve 
material  and  to  regard  the  non-protein 
compounds  as  those  momentarily  engaged 
in  nitrogenous  metabolism.  The  latter,  as 
I  have  indicated,  differ  greatly,  since  they 
include  both  nutritive  material  and  waste 
products ;  but  on  account  of  a  certain  simi- 
larity in  chemical  behavior  they  may  be  es- 
timated collectively,  and  when  grouped  in 
this  way  are  designated  as  the  non-protein 
nitrogen  of  the  blood. 

For  the  estimation  of  the  non-protein  ni- 
trogen a  remarkably  accurate  and  satis- 
factory method  was  devised  by  Folin«  We 
have  employed  it  in  35  cases  in  which  nor- 
mal pregnancy  concluded  with  a  sponta- 
neous delivery ;  we  found  in  the  case  of  the 
mother  an  average  of  25.2  mg.  of  non-pro- 
tein nitrogen  per  100  cc.  of  blood  and  in  the 
case  of  the  fetus  24.9  mg. 

The    impressive    resemblance    between 


THE  NUTRITION  OF  THE  FETUS    23 

these  figures  does  not  depend  upon  the  fact 
that  they  represent  a  mean  value.  The 
results  are  expressed  in  that  form  merely 
as  a  matter  of  convenience,  for,  examined 
individually,  the  cases  exhibit  the  same 
equality  of  maternal  and  fetal  non-protein 
nitrogen.  Thus,  in  20  cases  the  results  for 
the  two  organisms  did  not  differ  by  more 
than  a  milligram  and  in  the  others  the  dif- 
ference was  usually  less  than  two  milli- 
grams. The  most  instructive  illustration 
of  this  similarity  in  the  composition  of  ma- 
ternal and  fetal  blood  is  afforded  by  a  case 
of  twins  in  which  the  mother  presented  30 
mg.  and  each  infant  30.2  mg.  of  non-pro- 
tein nitrogen  per  100  cc.  of  blood. 

The  equality  of  the  non-protein  nitro- 
gen in  maternal  and  fetal  blood  indicates 
that  its  various  constituents,  belonging  in 
part  to  the  class  of  foods  and  in  part  to 
the  class  of  waste  products,  pass  freely 
through  the  placental  partition.  Indeed, 
our  findings  suggest  even  more  than  that. 
There  must  be  a  regulatory  mechanism 
which  maintains  the  same  concentration  of 
non-protein  nitrogen  in  the  two  circula- 
tions ;  and  such  a  strict  equality  of  concen- 
tration, we  are  at  a  loss  to  explain  on  any 


24    THE  NUTRITION  OF  THE  FETUS 

other  basis  than  that  of  simple  diffusion. 
This  process,  as  we  know,  permits  the 
ready  passage  of  certain  substances 
through  a  semi-permeable  membrane,  and 
to  secure  an  equal  concentration  on  both 
sides  of  the  partition  may  be  said  to  be  its 
very  aim.  However,  without  further  evi- 
dence of  a  more  detailed  character,  it 
would  be  hazardous  to  announce  a  final 
conclusion,  for  each  of  the  substances  in- 
cluded in  the  non-protein  nitrogen  should 
be  studied  separately.  As  that  has  been 
done,  we  may  proceed  to  examine,  indi- 
vidually, the  amino  acids,  urea,  ammonia, 
uric  acid  and  creatinine;  for,  besides  pro- 
tein, these  are  the  ingredients  of  the  blood, 
distinguished  by  the  fact  that  they  contain 
nitrogen. 


ly 

The  amino  acids  are  crystalline,  more  or 
less  soluble  compounds ;  and  on  account  of 
these  and  other  physical  and  chemical 
properties  they  would  be  expected  to  be 
diffusible  substances.  They  actually  are, 
as  Abel  showed  by  means  of  collodion 
tubes  ingeniously  contrived  to  accommo- 
date an  artifical  circulation  of  the  blood 
and  to  arrange  for  the  collection  of  sub- 
stances escaping  by  diffusion  through  the 
tube  wall.  Other  experimenters  have  con- 
firmed Abel's  statement  that  amino  acids 
pass  readily  across  such  a  permeable  par- 
tition, and  that  in  general  amino  acids  pass 
into  the  body  tissues  by  the  process  of 
diffusion. 

Until  very  recently,  it  was  not  suspected 
that  amino  acids,  supplied  by  the  mother, 
are  the  material  out  of  which  fetal  protein 
is  constructed.  Albumoses  were  thought 
to  serve  this  purpose,  for,  although  they 
were  not  demonstrable  in  either  maternal 
or  fetal  blood,  they  were  isolated  from  the 
placenta  itself.     These  findings  were  ac- 


26    THE  NUTRITION  OF  THE  FETUS 

cepted  in  support  of  the  view  that  the  pla- 
centa is  a  digestive  organ,  at  first  breaking 
down  maternal  protein  and  later  assem- 
bling   the    fragments    into    fetal   protein. 

AMINO  ACID  NITEOGEN 

OF   THE   PLASMA* 


Amino 

acid 

No. 

Source 

Para 

nitro- 
gen 
mg.per 
100  cc. 

Remarks 

1 

Mother 

Fetus 

I 

5.3 
7.0 

Remarks. 

2 

Mother 
Fetus 

n 

5.9 
7.9 

No  anaesthesia. 

3 

Mother 
Fetus 

m 

5.3 

7.8 

No  anaesthesia. 

4 

Mother 
Fetus 

IV 

6.5 

8.2 

No  anaesthesia. 

5 

Mother 
Fetus 

V 

7.2 
11.9 

No  anaesthesia. 

6 

Mother 

I 

5.6 

No  anaesthesia. 

Fetus 

7.6 

Premature  infant:  8th  month. 

7 

Mother 
Fetus 

n 

6.6 

8.3 

Whiffs  of  chloroform. 

8 

Mother 
Fetus 

n 

4.9 

6.8 

Whiffs  of  chloroform. 

9 

Mother 

Fetus 

I 

5.0 
6.4 

Whiffs  of  chloroform. 

10 

Mother 

Fetus 

I 

5.6 
7.3 

Morphine  and  tyramine. 

11 

Mother 

Fetus 

I 

4.5 
6.2 

Low  forceps:    Deep  chloroform. 

*^ Analyses  made  by  A.  H.  Morse. 


THE  NUTRITION  OF  THE  FETUS    27 

But  this  hypothesis  was  never  satisfactory 
and,  probably,  would  not  have  been  an- 
nounced if,  at  the  time,  it  had  been  kno^vn 
that  amino  acids  are  abundant  in  the  blood. 
The  proof  of  this  very  fundamental  fact 
wrought  revolutionary  changes  in  our  con- 
ception of  tissue  metabolism  and,  in  par- 
ticular, left  no  room  for  doubt  regarding 
the  elementary  substances  the  mother  con- 
tributes to  the  new  organism  for  the  manu- 
facture of  its  protein.  At  present,  there  is 
not  the  slightest  excuse  for  assuming  that 
the  placenta  synthesizes  protein  for  the  fe- 
tus. This  function  the  fetal  tissues  per- 
form for  themselves.  The  requisite  amino 
acids,  having  been  acquired  from  the 
mother,  are  available  in  the  fetal  blood. 
Of  this  we  are  sure ;  but  how  do  they  pass 
through  the  placental  partition!  Let  us 
see  what  light  blood  analysis  throws  upon 
the  subject. 

It  is  pertinent  that  the  blood  corpuscles 
are  richer  in  amino  acids  than  the  blood- 
plasma,  and  also  that  the  corpuscles  of  the 
fetus  are  richer  than  those  of  the  adult. 
What  part  these  facts  may  ultimately  play 
in  the  detailed  explanation  of  tissue  me- 
tabolism it  is  impossible  to  predict;  but  I 


28    THE  NUTEITION  OF  THE  FETUS 

am  doubtful  that  they  have  any  signifi- 
cance for  our  immediate  problem,  since 
only  substances  in  solution — substances  in 
the  plasma — take  part  in  the  placental  in- 
terchange. Furthermore,  though  many 
technical  intricacies  could  be  enumerated, 
perhaps,  it  is  sufficient  to  state  that  no 
analytical  method  at  hand  includes  all  of 
the  amino  acids  in  the  blood.  The  method 
devised  by  Van  Slyke  takes  into  account 
most  of  them  and  this  procedure  was  used 
in  our  investigations. 

An  excess  of  amino  acids  amounting  to 
about  2  mg.  of  nitrogen  appears  uniformly 
in  favor  of  the  fetal  plasma.  Even  such  a 
small  difference  in  concentration  implies 
that,  so  far  as  the  amino  acids  are  con- 
cerned, some  process  is  added  to  that  of 
simple  diffusion  in  the  regulatory  mechan- 
ism of  the  placental  interchange.  Similar 
results  in  connection  with  the  passage  of 
amino  acids  into  various  tissues  led  Van 
Slyke  to  give  the  name  ''absorption''  to 
the  phenomenon  in  question.  This  inves- 
tigator found  that  if  amino  acids  were  in- 
jected into  the  circulation  they  diffused 
into  the  tissues  rapidly  and  an  equilibrium 
was  reached  when  the  tissues  contained 


THE  NUTRITION  OF  THE  FETUS    29 

about  ten  times  as  much  amino  acid  nitro- 
gen as  the  plasma.  An  equilibrium  is 
reached  between  maternal  and  fetal  blood 
when  there  is  only  a  sHght  difference  of 
concentration  in  the  two  circulations,  while 
the  excess  of  amino  acids  in  fetal  plasma 
indicates  that  the  placenta  is  capable  of  ab- 
sorbing them  and  also  of  preventing  their 
departure  from  the  fetus. 


U>'riL  the  time  of  birth,  the  fetns  does 
not  einp-cy  the  same  chamiels  as  the  adult 
t;  ^t:  :i  :.  o:  the  excretory  products  formed 
by  the  utilization  of  food.  The  typical  ac- 
tio.:  ::  :h-  hiings.  for  example,  begins  when 
brra:h:i:z  becomes  established  in  the  new- 
': : m  :  previoiislv.  the  elimination  of  carbon 
d::jh:-.e  has  been  conducted  through  the 
jhs  :e:::a,  £.::i  this  gas,  after  reaching  the 
D:ot_-r's  oiroulation.  is  excreted  by  her 
Itins-s,  Siniilarlv.  the  placenta  takes  the 
pVs  :e  ::  the  iTtal  ^iiiieys.  ITrea,  ammonia, 
iirij  arhh  ■jr-atine  and  creatinine,  the 
~a.s:e  products  derived  from  the  use  of 
proteh„  7  the  fetus,  are  borne  back  to  the 
plaj-n:a.  transf-rreo.  from  the  fetal  to  the 
materiijh  :::  jilation  auh  nnally  thrown  off 
in  ziLr  m  t^-r  s  arine,  The  mechanism  re- 
sp'.n-ih'^  ::r  th-  transfer  of  these  sub- 
sta:::-s  from  one  oiraulation  to  the  other, 
ana  tnat  alone  is  of  interest  here,  becomes 
qnite  clear  in  the  light  of  blood  analysis, 
for  the  resnlts  obtained  in  this  way  estab- 
lish  the   fact   that   the   fetal  nitrogenous 


THE  xriEITIOy  OF  THE  FETUS     31 


'Jx 


u.~^  .  _^> 


waste  products  pass  throus-l 
in  accord  with  the  principle: 

Urea,  the  most  abundant  of  the  nitroir- 
enous  waste  products,  is  so  rea  ::."  :::- 
fusible  that  its  concentration  in  :„r    T:  . 


UEIC  ACID 


No. 

SoTirce 

Para 

tTric 

acid 

m^.per 

IW  cc. 

?-e~,irV3 

1 

Mother 

FeCns 

6.S 

5.0 

C]i::::::m, 

2 

Mother 
FetTis 

4.S 
4.0 

Chloroform. 

3 

Mother 
Feta3 

4.3 
4.3 

Chloro::?Tn. 

4 

Mother 

Fetus 

8.0 

8.: 

(    2.  I"- '''<'>"!' r.  1*  rn  . 

5 

Mother 

Fetus 

5.C 
5.6 

<- Luoro  form- 

6 

Mother 

Fetus 

n 

2.3 

2.5 

No  anafistbesia.     1 

7 

Mother 
Fetus 

n 

l.S 

1.3 

Chloroform. 

8 

Mother 

Fetus 

m 

2.2 
2^0 

No  aiia€aitlieai&.     | 

9 

Mother 
Fet-us 

ITT 

3.0 
3.3 

Clilosroform. 

10 

Mother 
Fetus 

IV 

2.0 
2.7 

CtdoccfaiiB.            1 

1 

11 

Mother 

Fetus 

V 

2.2 
2.4 

No  anaestlfe^a. 

12 

Mother 

Fet^is 

X 

2.8 

No  anaestliesla. 

Analyses  made  by  L.  J.  Soger 


32    THE  NUTRITION  OF  THE  FETUS 

plasma,  the  corpuscles  and  the  tissues  of 
our  bodies  is  always  the  same.  Conse- 
quently, before  the  facts  were  actually 
determined,  it  would  have  been  a  safe 
prediction  that  identical  quantities  of  urea 
would  be  found  per  unit  volume  of  the 
blood  of  each  organism.  Our  observations 
verify  this  prediction,  for  in  a  series  of  16 
normal  cases  the  results  gave  an  average 
of  10.5  mg.  of  urea  per  100  cc.  in  the  blood 
of  the  mother  and  10.4  mg.  in  the  fetus. 
Furthermore,  in  the  presence  of  a  compli- 
cation, as  nephritis,  where  a  relatively 
large  quantity  of  urea  occurs  in  the  mater- 
nal blood,  a  similar  value  obtains  in  the 
fetal  blood.  The  evidence  is  conclusive, 
then,  that  the  placenta  takes  no  active  part 
in  the  elimination  of  fetal  urea,  but  be- 
haves as  a  semi-permeable  membrane. 


"TOTAL"  CREATININE 

OP   THE   PLASMA 


Author 

Mother 
mg.  per  100  cc. 

Fetus 
mg.  per  100  cc. 

Number  of  Cases 

Hunter 

and 
Campbell 

Plass 

1.67 
1.70 

1.75 
1.73 

18 
12 

THE  NUTRITION  OF  THE  FETUS    33 

As  the  method  we  employed  to  deter- 
mine the  quantity  of  nrea  really  includes 
the  ammonia  which  is  present  in  the  blood 
in  extremely  small  amounts,  the  analytical 
results  just  referred  to  are  doubly  signifi- 
cant. They  make  it  certain  that  ammonia, 
as  well  as  urea,  passes  through  the  pla- 
centa by  diffusion.  That  the  same  expla- 
nation also  holds  for  uric  acid  is  clear  from 
our  figures  in  the  table  on  page  31;  and 
these  are  confirmed  by  the  results  of 
Kingsbury  and  Sedgwick.  Finally,  the 
evidence  regarding  creatinine  and  creatine 
which  have  been  studied  by  Hunter  and 
Campbell  and  by  Plass  agrees  perfectly 
with  the  conclusions  just  reached.  There- 
fore, we  are  confident  of  the  passive  role  of 
the  placenta  in  the  transmission  of  all  the 
nitrogenous  fetal  waste  products.  They 
enter  the  maternal  circulation  as  freely  as 
if  the  placenta  did  not  exist,  and  ordinarily 
the  estimation  of  the  quantity  of  them  in 
the  mother's  blood  holds  valid  for  the 
blood  of  the  fetus. 


VI 

Caebohydrate,  the  second  of  the  organic 
foodstuffs  to  be  studied,  becomes  avail- 
able for  intermediary  metabolism  in  the 
form  of  glucose,  the  blood  sugar.  An  excel- 
lent method  for  its  determination  devised 
by  Benedict  was  the  one  employed  in  our 
series  of  cases.  For  the  mother,  the  mean 
value  found  was  0.132%,  and  for  the  fetus 
0.115%.  Slightly  higher  values  occurred 
in  the  maternal  blood  in  19  of  our  24  cases, 
while  the  values  were  identical  in  both  cir- 
culations in  five  cases.  Bergsma  states 
that  the  sugar  content  of  the  blood  in  the 
two  organisms  is  always  the  same.  How- 
ever, his  work  is  open  to  criticism,  for  the 
specimen  from  the  mother  and  that  from 
the  infant  were  not  obtained  simultane- 
ously; in  some  instances  an  interval  of 
twenty  minutes  elapsed  between  the  times 
when  the  specimens  were  secured. 

These  facts  do  not  support  a  hypothesis 
requiring  the  action  of  a  placental  enzyme. 
That  doctrine  advocated  by  Hofbauer  rests 
chiefly    upon    his    demonstration    of    fer- 


No.  j  Source  Para 


Blood-sug-ar 


Remarks 


9 
10 
11 
12 
13 
14 
15 
16 
17 
18 
19 
20 
21 
22 
23 
24 


Mother 

Fetus 

Mother! 

Fetns    ! 

Mother! 

Fetus 

Mother 

Fetus    ! 

Mother! 

Fetus    I 

Mother 

Fetus    I 

Mother, 

Fetus    i 

Mother 

Fetus 

Mother 

Fetus 

Mother 

Fetus 

Mother 

Fetus 

Mother 

Fetus 

Mother 

Fetus 

Mother 

Fetus 

Mother 

Fetus    I 

Mother!    jjj 

Fetu_s    I 

Mother     jjji 

Fetus 

Mother 

Fetus 

Mother 

Fetus 

Mother 

Fetus 

Mother 

Fetus 

Mother 

Fetus 

Mother 

Fetus 

Mother'  y  1 1 1 

Fetu: 


I 
I 
I 
I 
I 
I 
I 
I 

n 
n 
n 
n 
n 
n 
n 


iv 

IV 

IV 

V 

V 

VI 


0.143 

0.124 

0.097 

0.10 

0.161 

0.131 

0.137 

0.141 

0.125 

0.108 

0.155 

0.112 

0.142 

0.106 

0.155 

0.124 

0.126 

0.11 

0.1.56 

0.124 

0.146 

0.108 

0.115 

0.103 

0.112 

0.086 

0.11 

0.075 

0.125 

LMul 

0.105 

0.096 

0.126 

0.105 

0.172 

0.122 

0.124 

0.095 

0.126 

0.094 

0.132 

0.112 

0.126 

0.13 

0.089 

0.06 

0.185 

0.185 


^VThiffs  of  chloroform, 

Morphine  and  tvi''amine. 

Morphine  and  tyraniine. 

Whiffs  of  chloroform. 

Whiffs  of  chloroform. 

Whiffs  of  chloroform. 

Whiffs  of  chloroform. 

Whiffs  of  chloroform. 

Xo  anaesthetic. 

Whiffs  of  chloroform. 

Whiff's  of  chloroform. 

Whiffs  of  chloroform. 

Whiffs  of  chloroform. 
!  Whiffs  of  chlorofoi-m. 
,  Whiffs  of  chloroform. 

Xo  anaesthetic.  | 

i 

Whiffs  of  chloroform. 

j  Whiffs  of  chloroform. 

I 

!  Whiffs  of  chloroform. 

Xo  anaesthetic.  ' 

Whiffs  of  chloroform. 

Xo  anaesthetic.  | 

Whiffs  of  chloroform, 

Whiffs  of  chloroform. 


*AnalTses  made  bv  W.  H.  Morriss. 


36    THE  NUTRITION  OF  THE  FETUS 

ments  whose  function,  in  all  probability, 
is  the  preparation  of  the  glycogen,  stored 
in  the  decidua,  for  passage  to  the  fetus. 
The  results  of  blood  analysis  certainly  do 
not  indicate  that  enzymes  are  responsible 
for  the  transportation  of  glucose  through 
the  placenta,  but,  on  the  contrary,  speak 
strongly  against  it.  Thus,  in  a  case  of 
double-ovum  twins,  where  each  fetus  had 
its  own  placenta,  the  blood  sugar  of  one 
was  0.099%  and  of  the  other  0.096%,  while 
that  of  the  mother  was  0.12%.  Such  find- 
ings are  inexplicable  except  on  the  basis  of 
diffusion,  and  on  this  basis  higher  maternal 
values  promote  a  steady  flow  of  glucose 
toward  the  fetus.  In  this  arrangement  to 
guarantee  an  adequate  supply  of  carbo- 
hydrate to  the  fetus  there  is  an  intimation 
of  its  great  importance  before  birth;  and 
when  we  learn,  as  we  shall,  that  this  infer- 
ence has  the  support  of  facts  regarding  the 
fats  and  lipoids,  it  becomes  even  more  ap- 
parent that  the  fetus  depends  to  an  un- 
usual degree  upon  the  maternal  contribu- 
tion of  glucose  for  the  maintenance  of  its 
nutrition. 


VII 

Fkom  a  long  series  of  observations  we 
obtained  analytical  data  relative  to  the  fats 
and  lipoids  which  is  illustrated  by  the  re- 
sults in  the  table.  These  substances  are 
more  abundant  in  the  mother  and  rela- 
tively large  maternal  values  are  accompa- 
nied by  large  fetal  values;  otherwise,  the 
most  notable  feature  of  our  findings  con- 
sists in  the  disparity  between  the  quanti- 
ties of  fats  and  lipoids  in  the  two  circula- 
tions. Between  the  plasmas  a  similar  dis- 
parity exists.  Here  the  difference  between 
the  maternal  and  the  fetal  figures  is  so 
great  that  we  may  not  entertain  the  possi- 
bility of  fat  passing  through  the  placenta 
in  the  way  other  substances  do.  Toward 
explaining  such  results  two  alternatives 
come  to  mind;  either  the  fats  and  lipoids 
cross  the  placenta  with  the  aid  of  an  en- 
zyme, or  they  do  not  cross  at  all.  Although 
our  data  would  accord  with  either  explana- 
tion, leaving  the  question  open,  there  are  at 
hand  observations  of  a  very  different  kind 
which  decide  the  matter  and  teach  that  the 
latter  interpretation  is  correct. 


»— t 
O 

I— f 

Q 

QQ 
P4 


Q 

?i 

O 

^ 

O 

o 

h-l 

o 

U^ 

I— 1 

» 

s* 

O 

S5. 

W 

. 

^ 

<=5 

g 

Wliiffs  of  chloroform. 
Whiffs  of  chloroform. 
Whiffs  of  chloroform. 

PLASMA 

(mg.  per  100  cc.) 

Whiffs  of  chloroform. 
Whiffs  of  chloroform. 
Wliiffs  of  chloroform. 

O  O  L'^  O  IC  O 

irt  !S  Lt  ic  -*  t- 
re  CI  re  ci  c<i  T-i 

o  o  o  o  o  o 

t^  O  CO  O  '^  1-1 

CI  cq  ci  ci  ci  1-1 

£ 

-t-> 
a) 

U 

Li  o  o  in  o  o 

CO  lO  ^+1  (M  CO  O 

T-t    1-i    1—i    T-i                »H 

O  O  O  O  O  Lt 
CI  LC  O  CO  CC'  cc 
r- 1  1— I  tH  T— 1 

lO  O  O  ITS  lO  m 

1-1  C1 1--.  CO  -t-  cq 

O  O  O  O  O  O 

00  CO  CO  ^  CO  ,-i 

1—1       1—)       1—1 

"3 

0  o  ir^  o  irt  o 
CO  t-  CO  CO  cq  cq 

01  1-1  Cl  ^.  Cl  f-i 

o  o  o  o  o  in 

O  CO  CO  t*  CD  Oi 
CO  1-i  CI  r-l  CI 

73 

O  O   Lt   Lt    O  lO 

CI  c:5  cc  i^  -r  t^ 

i-H  t-  GC  CO  C5  t> 

o  o  un  m  o  o 

•^  -^  ^  r-i  (O  oo 
Cl  CO  C5  L—  O  t^ 

1— ( 

o 

3 
o 

Mother 

Fetus 

Mother 

Fetus 

Mother 

Fetus 

Mother 

Fetus 

Mother 

Fetus 

Mother 

Fetus 

6 

^      cq      CO 

1— i          Cl          CO 

1 

CD 


THE  NUTEITION  OF  THE  FETUS     39 

Following  the  investigations  of  Hof- 
bauer  and  of  Gage,  Mendel  and  Daniels  re- 
sorted to  vital  staining  and  employed 
Sudan  III,  which  colors  fat  red.  The  an- 
imals selected,  preg-nant  rats,  were  treated 
by  injection  of  the  dye  into  the  maternal 
circulation.  Invariably,  as  these  investi- 
gators find,  the  maternal  fat  is  stained,  and 
not  the  fetal.  Between  the  tissue  affected 
and  that  not  affected  the  line  of  demarca- 
tion in  the  region  of  the  placenta  is  very 
sharp.  Stained  fat  cannot  be  traced  in 
transit  through  the  organ  and  there  is  no 
staining  of  the  fetal  fat.  Now,  these  obser- 
vations, especially  in  conjunction  with  the 
disparity  we  note  between  the  amount  of 
fat  in  the  blood  of  the  mother  and  that  of 
the  fetus,  demonstrate  in  a  convincing  way 
that  fat  is  not  included  among  the  mate- 
rials contributed  by  the  parent  to  her  off- 
spring. The  fat  of  the  body  of  the  fetus  is 
manufactured  there,  almost  certainly  man- 
ufactured from  carbohydrate  with  which 
the  new  organism  is  supplied  abundantly. 
In  theory,  then,  there  is  no  necessity  for 
fats  and  their  derivatives,  the  Lipoids,  to 
pass  the  placental  partition;  and  the  evi- 
dence gathered  both  from  biological  and 


40    THE  NUTRITION  OF  THE  FETUS 

chemical  studies  substantiates  our  conclu- 
sion that  they  have  no  part  in  the  placental 
interchange. 


VIII 

Without  certain  reservations,  we  may  not 
infer  that  what  we  have  found  true  for 
the  placental  interchange  at  full  term  also 
pertains  to  the  early  months  of  pregnancy, 
a  period  when  the  thickness  and  complex- 
ity of  the  walls  of  the  chorionic  villi  are 
notably  greater  than  they  are  later.  The 
simplification  of  the  placental  partition  oc- 
curs at  about  the  18th  to  20th  week  of  preg- 
nancy, and  this  date  marks  the  beginning 
of  a  more  rapid  rate  of  fetal  growth.  Dur- 
ing the  latter  part  of  pregnancy,  at  least, 
the  placental  partition  is  passive  and  be- 
haves like  a  semi-permeable  membrane; 
the  facts  at  hand,  in  other  words,  support 
the  mechanistic  hypothesis  of  placental 
function.  Thus,  the  amino  acids,  from 
which  fetal  protein  is  built,  and  glucose, 
which  supplies  the  requisite  energy  for  tis- 
sue construction,  pass  freely  to  the  new  or- 
ganism in  accord  with  the  principles  of  dif- 
fusion. While  in  the  mother's  blood,  these 
substances  are  not  more  accessible  to  her 
own  tissues  than  to  the  fetus ;  and  probably 


42    THE  NUTRITION  OF  THE  FETUS 

the  quantity  of  them  which  reaches  the 
fetus  is  regulated  by  the  rate  of  their  con- 
sumption in  its  body. 

The  interchange  of  water  between  the 
two  organisms  and  of  most,  if  not  of 
all,  of  the  inorganic  salts,  including  cal- 
cium, magnesium,  sodium,  and  potassium, 
takes  place  in  accord  with  the  principles 
of  diffusion.  With  regard  to  iron  it  is  im- 
possible, at  present,  to  affirm  what  ar- 
rangements are  made  for  its  transporta- 
tion through  the  placenta.  This  intricate 
and  unsolved  problem  occupies  a  unique 
position  among  the  factors  of  fetal  nutri- 
tion. Stored  in  the  newly  born  infant 
there  is  a  large  quantity  of  iron,  so  large, 
indeed,  that  the  quantity  is  proportion- 
ately much  greater  than  in  the  adult.  The 
purpose  of  this  storage  in  the  newborn, 
Bunge  believes,  is  to  compensate  for  the 
inadequate  amount  of  iron  in  human  milk. 

The  fats  and  lipoids  of  the  mother's 
blood,  as  we  have  seen,  are  held  in  check 
by  the  placenta;  the  fetus  manufactures 
fats  out  of  some  other  material,  most  likely 
out  of  the  glucose  contributed  by  the 
mother.  The  manifest  difference  between 
maternal  and  fetal  blood  in  this  respect 


THE  NUTRITION  OF  THE  FETUS     43 

stimulates  our  curiosity  with  regard  to  the 
fat  metabolism  of  pregnancy,  and  this  at- 
titude is  in  harmony  with  the  times,  for 
everywhere  at  present  there  is  a  lively  in- 
terest in  the  nutritional  role  of  the  fats  and 
the  lipoids,  cholesterol  and  lecithin.  The 
purpose  and  fate  of  the  latter,  physiolo- 
gists have  not  made  out  satisfactorily, 
even  with  regard  to  animal  metabolism  in 
general.  But,  tempting  as  speculation  is, 
at  the  moment  we  may  go  no  further  than 
the  facts ;  there  is  a  high  fat  content  in  the 
blood  of  the  pregnant  woman,  a  much 
lower  one  in  the  blood  of  the  fetus,  and  be- 
tween the  two  circulations  there  is  no  in- 
terchange of  fats  or  related  substances. 

All  fetal  waste  products,  including  car- 
bon dioxide,  which  was  the  first  to  be 
thoroughly  studied,  pass  the  placenta  by 
diffusion.  Active  elimination  of  these  sub- 
stances on  the  part  of  the  mother's  excre- 
tory organs  maintains  their  proper  concen- 
tration in  her  blood  and,  simultaneously, 
there  proceeds  a  steady  purification  of  the 
blood  of  the  fetus.  Less  favorable  condi- 
tions prevail  in  cases  of  nephritis  and  of 
organic  cardiac  disease  when  an  unusually 
large   amount   of   excretory  products   ap- 


44    THE  NUTRITION  OF  THE  FETUS 

pears  in  the  mother's  blood,  and  their 
concentration  in  both  maternal  and  fetal 
circulations  is  always  the  same.  It  is  not 
unlikely,  therefore,  that  in  the  presence  of 
such  maternal  complications  intra-uterine 
death  may  be  explained  on  the  basis  of  an 
inefficient  removal  of  fetal  waste. 


IX 

In  the  final  analysis,  the  nutrition  of  the 
fetus  involves  two  factors,  namely,  the 
peculiar  activity  of  its  own  organs  and  the 
supply  of  food  it  receives.  The  first  is  the 
more  fascinating,  and  also  the  more  dif- 
ficult of  study  because  the  isolation  of  the 
fetus  baffles  the  most  ingenious  experi- 
menters. In  the  absence  of  specific  knowl- 
edge regarding  the  intermediary  fetal  me- 
tabolism our  nearest  approach  to  the  facts 
is  to  accept  an  analogy  with  adult  nutri- 
tional processes.  And  yet,  in  doing  so,  we 
are  conscious  of  not  being  logical,  for  the 
unusual  prominence  of  certain  organs,  as 
the  th^Tnus  gland,  indicates  the  existence 
of  radical  differences  between  the  metab- 
olism of  the  immature  organism  and  that 
of  the  adult. 

The  second  factor  in  the  nutrition  of  the 
fetus — its  food  supply — has  been  brought 
within  the  range  of  direct  observations ; 
and  some  of  the  conclusions  derived  from 
the  study  of  the  origin  and  the  variety  of 
materials  incorporated  in  its  body  have  a 


46    THE  NUTRITION  OF  THE  FETUS 

practical  application.  Thus,  there  is  no 
diet  specifically  adapted  to  the  state  of 
pregnancy;  the  prospective  mother  may 
exercise  the  same  freedom  as  any  one  else 
in  the  selection  of  food.  She  should,  how- 
ever, choose  what  will  agree  with  her  and 
avoid  that  which  she  cannot  digest  and  as- 
similate. Personal  experience  in  the  main 
must  guide  everyone  as  to  what  to  eat  and 
most  women  follow  the  dictates  of  appetite 
after  they  become  pregnant  as  safely  as 
they  did  before. 

In  a  practical  sense  the  quantity  of  the 
mother's  food  is  more  influential  than  its 
quality.  Popular  opinion  holds  that  dur- 
ing pregnancy  the  mother  ^ '  should  eat  for 
two."  This  doctrine  is  erroneous.  A  diet 
which  has  previously  been  ample  will  like- 
wise be  sufficient  throughout  pregnancy. 
And  it  is  not  unimportant  to  emphasize 
this  view,  which  has  the  unqualified  sup- 
port of  painstaking,  scientific  investiga- 
tions, because  overeating  during  preg- 
nancy is  much  more  likely  to  provoke 
discomfort  than  insufficient  nourishment. 
On  the  other  hand,  there  can  be  no  justifi- 
cation for  measures  intended  to  restrict 
the  growth  of  the  fetus,  for  when  rigidly 


THE  NUTRITION  OF  THE  FETUS     47 

carried  out  they  tend  to  weaken  the 
mother.  She  may  be  careful,  in  other 
words,  to  avoid  overgrowth  of  the  fetus, 
but  should  not  adopt  a  diet  so  limited  as  to 
interfere  with  normal  development.  So 
long  as  her  health  is  properly  maintained 
no  thought  may  be  given  as  to  what  the 
size  of  the  fetus  is  likely  to  be.  At  present, 
provided  the  physician  determines  by  a 
thorough,  preliminary  examination  the  ex- 
istence of  any  disproportion  between  the 
size  of  the  fetus  and  the  capacity  of  the 
mother's  pelvis,  he  is  qualified  to  decide 
what  the  appropriate  treatment  should  be 
in  order  to  bring  pregnancy  to  a  successful 
termination. 


REFERENCES 

Gage.  S.  H.  and  S.  P. :  Coloration  of  the  milk  in 
laetating  animals  and  staining  of  the  growing 
adipose  tissne  in  the  suckling  young.  Anat. 
Record.  1909.  III.  203. 

Hunter  and  Campbell :  Placental  transmission 
of  creatinine  and  creatine.  Jour.  Biol.  Chem., 
191S.  xxxiv.  5. 

]\Iendel  and  Daniels :  Behavior  of  fat  soluble 
dyes  and  stained  fat  in  the  animal  organism. 
Jour.  Biol.  Chem.,  1912,  XIII,  71. 

Morriss :  The  obstetrical  significance  of  the 
blood-sugar  with  special  reference  to  the  pla- 
cental   interchange.      Bull.    Johns    Hopkins 

Hosp..  1917.  xxviii.  140. 

Morse :  The  amino-acid  nitrogen  of  the  blood  in 
cases  of  normal  and  complicated  pregnancy 
and  also  in  the  new-born  infant.  Bull.  Johns 
Hopkins  Hosp.,  1917.  xxviii,  199. 

Murlin:  Metabolism  of  mother  and  offspring. 
Am.  Jour.  Obst..  1917,  Ixx^^  913. 

Plass :  Placental  transmission :  Total  creati- 
nine in  plasma,  whole  blood  and  corpuscles 
of  mother  and  fetus.  Bull.  Johns  Hopkins 
Hosp..  1917.  xx\iii,  297. 


THE  NUTEITIOX  OF  THE  FETUS    49 

Slemons:  Analysis  of  the  blood  in  eclampsia 
and  allied  intoxications.  Am.  Joiir.  Obst., 
1918,  Ixx^'ii.  797. 

Slemons  and  Bogert.  The  uric  acid  content  of 
maternal  and  fetal  blood.  Jour,  of  Biol. 
Chem.,  1917,  xxxii,  63. 

Slemons  and  Curtis :  Cholesterol  in  the  blood 
of  mother  and  fetus :  a  preliminary  note.  Am. 
Jour.  Obst.,  1917.  Ixxt.  569. 

Slemons  and  Morriss :  The  non-protein  nitro- 
gen and  urea  in  the  maternal  and  fetal  blood 
at  the  time  of  birth.  Bull.  Johns  Hopkins 
Hosp.,  1916,  xx^ui.  343. 

Slemons  and  Stander :  The  fats  and  lipoids  in 
the  blood  of  mother  and  fetus.  Trans.  Am. 
Soc.  for  Advancement  of  Clinical  Investiga- 
tion, 1918. 

"Wilson :  Nitrogen  metabolism  during  preg- 
nancy. Bull.  Johns  Hopkins  Hosp..  1916. 
xxrv^i,  121. 


COLUMBIA   UNIVERSITY   LIBRARIES 

This  book  is  due  on  the  date  indicated  below,  or  at  the 
expiration  of  a  definite  period  after  the  date  of  borrowing,  as 
provided  by  the  library  rules  or  by  special  arrangement  with 
the  Librarian  in  charge. 

DATE  BORROWED 

DATE  DUE 

DATE  BORROWED 

DATE  DUE 

DATE  DUE 


RCrhtro 


SL?v 


4/); 


